The invention relates to a recording medium for the reproduction of patterns with high resolution. The invention is directed in this respect particularly to the recording of large quantities of data per square millimeter (mm.sup.2). The invention moreover relates to a method for producing such recording media with high resolution patterns.
With the aid of microfilm techniques, large volumes of archives (libraries, drawings and other documents) may be stored in a very small space. The limits of microfilm reside in the resolution capacity of the image or of the recording films, that is, in the legibility of the recorded image following re-enlargement to approximately the dimensions of the original picture. One limit to the resolution of conventional microfilm is the result of the grain of the photographic emulsions used, which are typically 10 to 20 microns in diameter. In this connection, the resolution of photographic fine grain layers as indicated by the manufacturers does not provide a simple indication of the resolution of microfilm. The manufacturers measure resolution in lines per millimeter, that is, the finest reproduceable grid as determined photometrically. The photometer curve of such an exposed grid distinctly shows maxima and minima. However, substantially more distinct contrasts are required for microfilm legibility, and these contrasts should be in black and white as far as possible and not in shades of gray. For exact documentation more or less sharp edges are needed. This means that the resolution indicated by the film manufacturer is much greater than the actual resolution of conventional microfilm.
Moreover, microfilms known to the prior art also may exhibit instability with respect to time, heat and light. Due to the shrinkage of the gelatin emulsion, patterns recorded thereon may be distorted with time and the films themselves may be distorted by heat. In color films the color of recorded images is subject to fading when exposed to light.
Photo-sensitized layers made from high polymers known as photo-resists offer the potential of substantially higher resolution than that obtained with photographic fine grain layers. By exposure to actinic light or with electrodes or ions, the chemical structure of these resists may be modified. In particular such exposure may change the solubility of the photo resist in specific "developer solutions".
The methods of "microphoto lithography" are well known in the prior art and have been applied in optics for the production of precise structures, such as graduated plates and graduations (see German Pat. No. 902,713). Of late they also have been used in semi-conductor technology in the so-called planar method for the fabrication of micro circuits. Likewise, lengthy messages (such as the text of the Bible, or highly reduced messages of U.S. Presidents with regard to the moon flight, etc.) have been produced on chrome-plated glass supports, with the aid of said micro lithography.